-LRB- CNN -RRB- ISIS militants in northern Syria released 19 Assyrian Christian hostages Sunday , an activist group said .

According to the London-based Syrian Observatory for Human Rights , all but one of the hostages were among the at least 220 Assyrians captured on February 23 during an attack on villages in the northern Syrian province of al-Hasakah .

The Syrian Observatory had said previously that a self-proclaimed ISIS court ordered the release of 29 Assyrian Christian hostages , citing an Assyrian commander .

The reasoning behind the release was not immediately clear . It was also not clear why only 19 people were let go Sunday .

The `` court '' told the commander that the fate of the other kidnapped Assyrians has yet to be decided by ISIS Sharia jurists .

When the decision was announced that at least some of the hostages would be released , Graeme Wood , with The Atlantic , said he was pleased to hear about it , but not entirely surprised .

`` ISIS has claimed for a long time to follow rules , and it claims that these Sharia courts will impose limits , '' he told CNN . `` They can attempt to get credibility by showing that they follow rules and that they have some kind of transparent process that follows their particular implementation of Sharia law . ''

Also this weekend , the Syrian Observatory reported that ISIS has killed 1,969 people , since the declaration of its `` caliphate '' last June . Nearly two-thirds of them -- 1,238 people -- were civilians .

Six were children and eight were women , the group said .

Of the rest , 95 were fighters from the al Qaeda-affiliated rebel group al-Nusra Front , the Syrian Observatory said , and 511 were officers and soldiers of regime forces .

ISIS also executed 125 of its own members for `` exceeding the limits in religion , '' the Syrian Observatory said .

`` We in SOHR believe that the real number of people that had been killed by -LRB- ISIS -RRB- is higher than the number documented by SOHR because there are hundreds of missing and detainees inside the -LRB- ISIS -RRB- jails , loss of communication with about 1,000 men of al-Shaitaat tribe , -LRB- and -RRB- dozens of Kurds who have still been missing '' since ISIS attacked the Syrian town of Kobani in September .

Samira Said reported from Abu Dhabi . Dana Ford reported and wrote from Atlanta . CNN 's Melissa Gray also contributed to this report .

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It 's unclear what will become of the other kidnapped Assyrians

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Syrian Observatory : ISIS has executed nearly 2,000 people since June